Has anyone got any tips about micing a whistle? I want to have on-stage control over the shape of the sound. This means I need a pedal or a small mixer that takes an XLR in and an XLR out?

What kind of shaping?

AFAIK, and I have looked, there are no pedals that work with microphone level signals.

The traditional method for controlling volume is to set the mic up for the loudest volume, and then move away from it to get quieter.

Too bad this is such an old thread.
I've used TC Helicon to control my flute/whistle mic for years. A bomb-proof pedal that shapes and provides power to condenser mics:
https://www.tc-helicon.com/Categories/T ... rans(en|en)
To this pedal, I've added a small pedal board that includes reverb and a looper, which I use mostly for practice.

So, yes, there are many solutions to adding effects and control to whistle mics.

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I’m using a TC Helicon personal monitor / processor for everything. Best piece of gear I have, apart from instruments. The effects are subtle... a smidge of de-essing, compression, and reverb even works with really trad situations. Sounds like me, only better.

Ok, the beer holder that clamps on to a mic stand is pretty good, too.

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whistletutor explains what is in his gig bag. Mics etc.

https://www.youtube.com/watch?v=FilIifmtmGk